Animal models of human disease that exploit the power of genetics offer a powerful tool to understand and cure diseases. One of the most widely used genetic animal models is the zebrafish. However, its use has largely been restricted to the analysis of development. Relatively few studies have utilized the mature fish even though many human diseases occur after development. For neurological studies, it is important to be able to analyze neuronal function in vivo. Imaging and electrophysiological recording are the predominant methods to do so. Unfortunately, there are essentially no studies on genetically altered adult zebrafish using these methods. These proposed studies will develop the technology to enable in vivo imaging as well as electrophysiological recording from the brain of living adult zebrafish and provide initial results using in vivo imaging. There are 4 goals: 1) Develop a stereotactic style head holder to immobilize the cranium and protocols to maintain the fish for several hours. This will include electrophysiological recording of evoked unit activit in tectum to demonstrate stability and physiological viability. 2) Using available zebrafish lines, GFP labeled optic fibers or Kaede labeled neurons will be imaged in the tectum of adult fish through a cranial opening for several hours using a 2 photon laser scanning microscope. 3) Generate zebrafish that are transparent as adults that have fluorescent optic fibers or tectal neurons. 4) Image these transparent adult zebrafish through the closed cranium using 2 photon microscopy and revive these fish for second imaging session. This project will demonstrate the feasibility of studying real time structural plasticity in living adult zebrafish thereby opening u a new animal model for these studies. This new model can take advantage of a large genetic base, an extensive background of developmental studies and a system that is far less costly than mice. Since adult fish show robust recovery of function following CNS injuries, planned future work using this model to study plasticity may provide insight into understanding and stimulating recovery in the human following CNS injuries and diseases.